On Thu 03-02-22 18:00:07, John Hubbard wrote:
> Remove a quirky special case from follow_pfn_pte(), and adjust its
> callers to match. Caller changes include:
>
> __get_user_pages(): Regardless of any FOLL_* flags, get_user_pages() and
> its variants should handle PFN-only entries by stopping early, if the
> caller expected **pages to be filled in. This makes for a more reliable
> API, as compared to the previous approach of skipping over such entries
> (and thus leaving them silently unwritten).
>
> move_pages(): squash the -EEXIST error return from follow_page() into
> -EFAULT, because -EFAULT is listed in the man page, whereas -EEXIST is
> not.
>
> Cc: Peter Xu <peterx@xxxxxxxxxx>
> Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> mm/gup.c | 13 ++++++++-----
> mm/migrate.c | 7 +++++++
> 2 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 80229ecf0114..2df0d0103c43 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -464,10 +464,6 @@ static struct page *no_page_table(struct vm_area_struct *vma,
> static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
> pte_t *pte, unsigned int flags)
> {
> - /* No page to get reference */
> - if (flags & (FOLL_GET | FOLL_PIN))
> - return -EFAULT;
> -
> if (flags & FOLL_TOUCH) {
> pte_t entry = *pte;
>
> @@ -1205,8 +1201,15 @@ static long __get_user_pages(struct mm_struct *mm,
> } else if (PTR_ERR(page) == -EEXIST) {
> /*
> * Proper page table entry exists, but no corresponding
> - * struct page.
> + * struct page. If the caller expects **pages to be
> + * filled in, bail out now, because that can't be done
> + * for this page.
> */
> + if (pages) {
> + ret = PTR_ERR(page);
> + goto out;
> + }
> +
> goto next_page;
> } else if (IS_ERR(page)) {
> ret = PTR_ERR(page);
> diff --git a/mm/migrate.c b/mm/migrate.c
> index c7da064b4781..be0d5ae36dc1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1761,6 +1761,13 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> continue;
> }
>
> + /*
> + * The move_pages() man page does not have an -EEXIST choice, so
> + * use -EFAULT instead.
> + */
> + if (err == -EEXIST)
> + err = -EFAULT;
> +
> /*
> * If the page is already on the target node (!err), store the
> * node, otherwise, store the err.
> --
> 2.35.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
